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Abstract:

A method and apparatus for extracting CO2 from air comprising an
anion exchange material formed in a matrix exposed to a flow of the air,
and for delivering that extracted CO2 to controlled environments.
The present invention contemplates the extraction of CO2 from air using
conventional extraction methods or by using one of the extraction methods
disclosed; e.g., humidity swing or electro dialysis. The present
invention also provides delivery of the CO2 to greenhouses where
increased levels of CO2 will improve conditions for growth.
Alternatively, the CO2 is fed to an algae culture.

Claims:

1-46. (canceled)

47. A method for the capture of CO2 from air, comprising the steps
of exposing an anion exchange material to a flow of air; and releasing
CO2 captured by said anion exchange material by wetting or a swing
in humidity, wherein said method is accomplished without any direct
energy input other than energy to move said anion exchange material.

48. The method of claim 47, further comprising continuously cycling said
anion exchange material between exposure to air and release of captured
CO.sub.2.

49. The method of claim 47, wherein said anion exchange material captures
CO2 when exposed to lower humidity and releases CO2 when
exposed to higher humidity.

50. The method of claim 47, wherein said anion exchange material is a
component of a heterogeneous ion exchange material.

54. The method of claim 47, wherein said released CO2 is transferred
to a sorbent.

55. The method of claim 54, wherein said sorbent is selected from the
group consisting of: a liquid amine, an ionic liquid, a solid CO2
sorbent, a lithium zirconate, a lithium silicate, a magnesium hydroxide,
and a calcium hydroxide.

[0002] The present invention in one aspect relates to removal of selected
gases from air. The invention has particular utility for the extraction
and sequestration of carbon dioxide (CO2) from air and will be
described in connection with such utilities, although other utilities are
contemplated.

BACKGROUND OF THE INVENTION

[0003] There is compelling evidence to suggest that there is a strong
correlation between the sharply increasing levels of atmospheric CO2
with a commensurate increase in global surface temperatures. This effect
is commonly known as Global Warming. Of the various sources of the
CO2 emissions, there are a vast number of small, widely distributed
emitters that are impractical to mitigate at the source. Additionally,
large scale emitters such as hydrocarbon-fueled power plants are not
fully protected from exhausting CO2 into the atmosphere. Combined,
these major sources, as well as others, have lead to the creation of a
sharply increasing rate of atmospheric CO2 concentration. Until all
emitters are corrected at their source, other technologies are required
to capture the increasing, albeit relatively low, background levels of
atmospheric CO2. Efforts are underway to augment existing emissions
reducing technologies as well as the development of new and novel
techniques for the direct capture of ambient CO2. These efforts
require methodologies to manage the resulting concentrated waste streams
of CO2 in such a manner as to prevent its reintroduction to the
atmosphere.

[0004] The production of CO2 occurs in a variety of industrial
applications such as the generation of electricity power plants from coal
and in the use of hydrocarbons that are typically the main components of
fuels that are combusted in combustion devices, such as engines. Exhaust
gas discharged from such combustion devices contains CO2 gas, which
at present is simply released to the atmosphere. However, as greenhouse
gas concerns mount, CO2 emissions from all sources will have to be
curtailed. For mobile sources the best option is likely to be the
collection of CO2 directly from the air rather than from the mobile
combustion device in a car or an airplane. The advantage of removing
CO2 from air is that it eliminates the need for storing CO2 on
the mobile device.

[0005] Extracting carbon dioxide (CO2) from ambient air would make it
possible to use carbon-based fuels and deal with the associated
greenhouse gas emissions after the fact. Since CO2 is neither
poisonous nor harmful in parts per million quantities, but creates
environmental problems simply by accumulating in the atmosphere, it is
possible to remove CO2 from air in order to compensate for equally
sized emissions elsewhere and at different times.

[0006] Most prior art methods, however, result in the inefficient capture
of CO2 from air because these processes heat or cool the air, or
change the pressure of the air by substantial amounts. As a result, the
net loss in CO2 is negligible as the cleaning process may introduce
CO2 into the atmosphere as a byproduct of the generation of
electricity used to power the process.

[0007] Various methods and apparatus have been developed for removing
CO2 from air. For example, we have recently disclosed methods for
efficiently extracting carbon dioxide (CO2) from ambient air using
capture solvents that either physically or chemically bind and remove
CO2 from the air. A class of practical CO2 capture sorbents
include strongly alkaline hydroxide solutions such as, for example,
sodium or potassium hydroxide, or a carbonate solution such as, for
example, sodium or potassium carbonate brine. See for example published
PCT Application PCT/US05/29979 and PCT/US06/029238.

[0008] There are also many uses for sequestered CO2. This includes
the use of CO2 in greenhouses where higher levels of CO2
contribute to increased plant growth. CO2 may also be supplied to
algae cultures. Researchers have shown that algae can remove up to 90% of
gaseous CO2 from air streams enriched in CO2 and can also
reduce the CO2 concentration in ambient air.

SUMMARY OF THE INVENTION

[0009] The present invention provides a system, i.e. a method and
apparatus for extracting carbon dioxide (CO2) from ambient air and
for delivering that extracted CO2 to controlled environments.

[0010] In a first exemplary embodiment, the present invention extracts
CO2 from ambient air and delivers the extracted CO2 to a
greenhouse. Preferably, the CO2 is extracted from ambient air using
a strong base ion exchange resin that has a strong humidity function,
that is to say, an ion exchange resin having the ability to take up
CO2 as humidity is decreased, and give up CO2 as humidity is
increased. Several aspects of this invention can also be used to transfer
CO2 from the collector medium into the air space of a greenhouse
where the CO2 is again fixed in biomass. In a preferred embodiment
of the invention, CO2 is extracted from ambient air using an
extractor located adjacent to a greenhouse, and the extracted CO2 is
delivered directly to the interior of the greenhouse for enriching the
greenhouse air with CO2 in order to promote plant growth.

[0011] In a second exemplary embodiment, this invention allows the
transfer of CO2 from a collector medium into an algae culture, where
the CO2 carbon is fixed in biomass. The algae biomass can then be
used for the production of biochemical compounds, fertilizer, soil
conditioner, health food, and biofuels to name just a few applications or
end-uses.

[0012] This invention also discloses transfer of CO2 in gaseous phase
and as a bicarbonate ion. In one embodiment, a calcareous algae is used
which creates calcium carbonate CaCO3 internally, and precipitates
the CaCO3 out as limestone.

[0013] Accordingly, in broad concept, the present invention extracts
CO2 from ambient air using one of several CO2 extraction
techniques as described, for example, in our aforesaid PCT/US05/29979 and
PCT/US06/029238. Where a carbonate/bicarbonate solution is employed as
the primary CO2 sorbent, the CO2 bearing sorbent may be used
directly as a feed to the algae. Where the CO2 is extracted using an
ion exchange resin as taught, for example in our aforesaid
PCT/US06/029238 application, the CO2 is stripped from the resin
using a secondary carbonate/bicarbonate wash which then is employed as a
feed to the algae. In a preferred alternative embodiment, the carbonate
is fed to the algae in a light enhanced bioreactor.

[0014] Thus, the present invention provides a simple, relative low-cost
solution that addresses both CO2 capture from ambient air and
subsequent disposal of the captured CO2.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Further features and advantages of the present invention will be
seen from the following detailed description, taken in conjunction with
the accompanying drawings, wherein

[0016]FIG. 1 is a block flow diagram illustrating the use of humidity
sensitive ion exchange resins in accordance with the present invention;

[0017] FIGS. 2a and 2b are schematic views of a CO2
extractor/greenhouse feeder in accordance with the present invention,
where filter units are located adjacent an exterior wall;

[0018] FIGS. 3a and 3b are schematic views of a CO2
extractor/greenhouse feeder in accordance with the present invention,
where filter units are located adjacent to the roof of the greenhouse;

[0019]FIG. 4 is a schematic view of a CO2 extractor/greenhouse
feeder showing an arrangement of filter units according the present
invention;

[0020]FIG. 5 is a schematic view of a CO2 extractor/greenhouse
feeder showing filter units arranged on a track according to an
alternative embodiment of the present invention;

[0021]FIG. 6 is a schematic view of a CO2 extractor/greenhouse
feeder including convection towers according to an alternative embodiment
of the present invention;

[0022]FIG. 7 is a schematic view of a CO2 extractor and algae
culture according to the present invention utilizing a humidity swing
applied to a collector medium;

[0023] FIG. 8 is a schematic view of a CO2 extractor and algae
culture according to the present invention utilizing a humidity swing
applied to a collector solution;

[0024] FIG. 9 is a schematic view of a CO2 extractor and algae
culture according to the present invention transferring gaseous CO2
by an electro-dialysis process;

[0025] FIG. 10 is a schematic view of a CO2 extractor and algae
culture according to the present invention transferring bicarbonate by an
electro-dialysis process;

[0026]FIG. 11 is a schematic view of a CO2 extractor and algae
culture according to the present invention utilizing an algae culture for
collector regeneration;

[0027] FIG. 12 is a schematic view of a CO2 extractor and algae
culture similar to FIG. 11 utilizing a nutrient solution;

[0028] FIG. 13 is a schematic view of a CO2 extractor and algae
culture according to the present invention utilizing a gas-permeable
membrane;

[0029] FIG. 14 is a schematic view of a CO2 extractor and algae
culture according to the present invention utilizing an anion-permeable
membrane;

[0030] FIG. 15 is a schematic view of a CO2 extractor and algae
culture similar to FIG. 14;

[0031]FIG. 16 is a schematic view of a CO2 extractor and algae
culture according to the present invention including a shower; and

[0032] FIG. 17 is a schematic view of a CO2 extractor and algae
culture similar to FIG. 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] In broad concept, the present invention in one aspect extracts
carbon dioxide from ambient air using a conventional CO2 extraction
method or one of the improved CO2 extraction methods disclosed in
our aforesaid PCT Applications, or disclosed herein, and releases at
least a portion of the extracted CO2 to a closed environment.

[0034] In a first exemplary embodiment, this closed environment is a
greenhouse. Preferably, but not necessarily, the CO2 extractor is
located adjacent to the greenhouse and, in a preferred embodiment the
extractor also provides shading for crops grown in greenhouses which are
sensitive to strong sunlight, and/or reduces cooling requirements for the
greenhouse.

[0035] In one approach to CO2 capture, the resin medium is
regenerated by contact with the warm highly humid air. It has been shown
that the humidity stimulates the release of CO2 stored on the
storage medium and that CO2 concentrations between 3% and 10% can be
reached by this method, and in the case of an evacuated/dehydrated
system, close to 100% can be reached. In this approach the CO2 is
returned to gaseous phase and no liquid media are brought in contact with
the collector material.

[0036] The CO2 extractor is immediately adjacent to the greenhouse
and is moved outside the greenhouse to collect CO2 and moved into
the greenhouse to give off CO2. In such embodiment, the CO2
extractor preferably comprises a humidity sensitive ion exchange resin in
which the ion exchange resin extracts CO2 when dry, and gives the
CO2 up when exposed to higher humidity. A humidity swing may be best
suited for use in arid climates. In such environment the extractor is
exposed to the hot dry air exterior to the greenhouse, wherein CO2
is extracted from the air. The extractor is then moved into the warm,
humid environment of the greenhouse where the ion exchange resin gives up
CO2. The entire process may be accomplished without any direct
energy input other than the energy to move the extractor from outside to
inside the greenhouse and vice versa.

[0037] Ion exchange resins are commercially available and are used, for
example, for water softening and purification. We have found that certain
commercially available ion exchange resins which are humidity sensitive
ion exchange resins and comprise strong base resins, advantageously may
be used to extract CO2 from the air in accordance with the present
invention. With such materials, the lower the humidity, the higher the
equilibrium carbon loading on the resin.

[0038] Thus, a resin which at high humidity level appears to be loaded
with CO2 and is in equilibrium with a particular partial pressure of
CO2 will exhale CO2 if the humidity is increased and absorb
additional CO2 if the humidity is decreased. The effect is large,
and can easily change the equilibrium partial pressure by several hundred
and even several thousand ppm. The additional take up or loss of carbon
on the resin is also substantial if compared to its total uptake
capacity.

[0039] There also seems to be an effect on humidity on the transfer
coefficient, i.e. the reaction kinetics seem to change with changing
humidity. However, the measured flux in and out of the resin seems to
depend strongly on the difference between the actual partial pressure and
the thermodynamic equilibrium pressure. As the equilibrium pressure
changes with humidity, the size of the flux can be affected without an
actual change in the reaction kinetics.

[0040] In addition, it is possible that kinetics is affected by other
issues. For example, ion exchange materials which we have found to be
particularly useful, are Anion 1-200 ion exchange membrane materials
available from Snowpure LLC, of San Clemente, Calif. The manufacturer
describes Anion 1-200 ion exchange membrane material as a strong base,
Type 1 functionality ion exchange material. This material, which is
believed made according to the U.S. Pat. No. 6,503,957 and is believed to
comprise small resin charts encapsulated--or partially encapsulated--in
an inactive polymer like polypropylene. We have found that if one first
hydrates this material and then dries it, the material becomes porous and
readily lets air pass through. The hydration/dehydration preparation is
believed to act primarily to swell the polypropylene binder, and has
little or no permanent effect on the resin, while the subsequent humidity
swings have no observed impact on the polypropylene binder. We have found
that these strong base ion exchange resin materials have the ability to
extract CO2 from dry air, and give the CO2 out when humidity is
raised without any other intervention. The ability of these materials to
extract CO2 directly from the air, when dry, and exhale the CO2
as humidity is raised, has not previously been reported.

[0041] As noted supra, it is necessary to first hydrate this material and
then dry it, before using, whereupon the material becomes porous and
readily lets air pass through. Before hydration, the membrane material is
substantially non-porous, or at least it is unable to permit passage of
an appreciable amount of air through the membrane. However, after
hydration and drying, the material is believed to undergo irreversible
deformation of the polypropylene matrix during the resin swelling under
hydration. Once the material has been deformed, the polypropylene matrix
maintains its extended shape even after the resin particles shrink when
drying. Thus, for substantially non-porous materials such as the Snowpure
Ion Exchange material above described, it is necessary to precondition
the material by hydrating and then drying the material before use.

[0042] We have observed a large change in the equilibrium partial pressure
of CO2 over the resin with a change in humidity. Humidity either
changes the state of the resin, or alternatively the entire system that
needs to be considered is the CO2/H2O resin system. While not
wishing to be bound by theory, it is believed that the free energy of
binding CO2 to the resin is a function of the H2O partial
pressure with which the resin is in equilibrium.

[0043] This makes it possible to have resins absorb or exhale CO2
with a simple swing in humidity without the need to resort to thermal
swing and/or pressure swing, which would add to energy costs which could
have an unfavorable effect with regard to the overall carbon dioxide
balance of the system.

[0044] The amount of water involved in such a swing appears to be quite
small. The possibility of a humidity swing also allows us to recover
CO2 from an air collector with minimal water losses involved.

[0045] Other strong base Type 1 and Type 2 functionality ion exchange
materials are available commercially from a variety of venders including
Dow, DuPont and Rohm and Haas, and also advantageously may be employed in
the present invention, either as available from the manufacturer, or
formed into heterogeneous ion-exchange membranes following, for example,
the teachings of U.S. Pat. No. 6,503,957.

[0046]FIG. 1 illustrates a first embodiment of our invention. A primary
ion exchange filter material 4 is provided in a recirculation cycle. A
primary pump 1 or a secondary pump (not shown) is used to remove the bulk
of the air in the system while valve V1 is open and push it out
through the air exhaust 2. At this point valve V1 is closed and a
secondary ion exchange capture resin is switched into the system by
opening valves V2 and V3. The secondary ion exchange resin can
be utilized to provide humidity and possibly some heat. Warm steam
stimulates the release of CO2 from the primary ion exchange filter
material 4, which is then captured on the secondary ion exchange resin
which is still out of equilibrium with the CO2 partial pressure. The
volume of water in the system remains small as it is recirculated and not
taken up by the secondary resin. While CO2 is unloading from the
primary ion exchange resin material 14 and being absorbed by the
secondary ion exchange resin, the bulk of the water cycles through the
apparatus. The amount of water that can be devolved or absorbed is much
smaller than the amount of CO2 that is transferred. At the end of
the cycle the primary ion exchange filter material 14 is refreshed and
the secondary ion exchange capture resin is loaded with CO2.

[0047] This system could be used to transfer CO2 from the air capture
medium, e.g. an ion exchange resin onto a secondary resin without washing
or wetting the primary resin. This has two advantages. First, the primary
resin is not directly exposed to chemicals such as amines that were used
in the past and described in our aforesaid PCT Application
PCT/US061/029238. Second, we have seen that wet resins are ineffective in
absorbing CO2 until they have dried out. It is therefore
advantageous to avoid the wetting of the material and thus operate in
this fashion where the resin is washed with low-pressure steam. Steam
pressures could be less than 100 Pa and thus be saturated at temperatures
similar to ambient values. However, the CO2 exchange is obviously
accelerated at higher temperatures and higher steam pressures. The
disadvantage of raising temperatures would be additional energy
consumption.

[0048] The design outlined here is a special example of a broader class of
designs where the secondary resin is replaced with any other sorbent
material that is capable of absorbing CO2 without absorbing water.
Such sorbents may include liquid amines, ionic liquids, solid CO2
sorbents such as lithium zirconate, lithium silicate, magnesium hydroxide
or calcium hydroxide, or any of a wide class of chemical or physical
sorbents capable of absorbing CO2 from a gas mixture including water
vapor and CO2. The central concept is that of using a humidity
swing, rather than a pressure or temperature swing to remove CO2
from the primary sorbent without bringing it in direct physical contact
with a secondary sorbent.

Application in a Greenhouse for Improving Crop Yields

[0049] As noted supra, crop yield in greenhouses can be improved by
increasing the carbon dioxide level in the greenhouse air. The present
invention provides for the introduction of carbon dioxide into a
greenhouse without combusting fuels emitting fossil fuel CO2 into
the air. More particularly, we have found that we can employ humidity
sensitive ion exchange resins to capture CO2 from dry outside air,
and then release the CO2 into the greenhouse by exposing the resins
to the warm moist greenhouse air.

[0050] In greenhouses located in warm in desert climates such as found in
the Southwest United States, the outside CO2 loading may be
performed at night when outside temperatures are cooler which may enhance
CO2 uptake capacity. In cooler climates where greenhouses rely in
part on radiative heating, our system of CO2 loading avoids the need
to let in cold air to replenish the CO2 and thus reduces the need
for heating employing fossil fuel consumption until temperatures drop so
low that fuel based heating becomes necessary.

[0051] In one embodiment, we employ several filters made from humidity
sensitive ion exchange active material. In one part of the cycle the
filters are exposed to outside air that could be driven by natural wind
flow, by thermal convection, or fans. It is preferable to avoid fans as
they add an unnecessary energy penalty. In a second part of the cycle,
moist air from inside the greenhouse preferably is driven through the
filter material, e.g. by fans, which then releases CO2 into the
greenhouse atmosphere. Since the climate control of the greenhouse
typically will rely on a fan system anyway, there is little or no energy
penalty.

[0052] Since plants at night respire, in some greenhouse designs it is
possible to strip the CO2 from the greenhouse air by pulling the
greenhouse air through the filters. The filters can then be exposed to
higher humidity to facilitate the daytime release of the CO2 into
the greenhouse.

[0053] In one embodiment, as shown in FIGS. 2A and 2B, the filter units 10
are located adjacent an exterior wall 12 of a greenhouse, and outside air
or greenhouse air routed selectively therethrough, as the case may be,
via pivotally mounted wall panels 14. Alternatively, as shown in FIGS. 3A
and 3B, the filter material 10 may be located exterior to and adjacent
the roof 18 of the greenhouse, and outside air or greenhouse air routed
selectively therethrough, as the case may be, via pivotally mounted roof
panels 20.

[0054] In yet another embodiment of the invention, shown in FIG. 4, the
filter units 10, can be moved from outside the greenhouse where they
extract CO2 from the air to inside the greenhouse where they release
the captured CO2. One possible option for doing this is to have
filter units mounted to pivotally mounted wall or roof panels 22 which
can be reversed so that a filter unit on the outside of the greenhouse is
exposed to the inside of the greenhouse and vice versa. Filter units that
are inside the greenhouse can have air blown through them by a fan
system. Filter units on the outside are exposed to ambient air. In a
preferred embodiment, shown in FIG. 4, the filter units 10 on the outside
are located adjacent the bottom end of a convection tower 24 that is
solar driven. Preferably the inlets are installed at the bottom end of
the convection towers where cool air enters and flows up the towers
through natural convection.

[0055] In yet another embodiment, shown in FIG. 5, the filter units 10 are
moved in and out of the greenhouse, e.g. suspended from a track 26.

[0056] Referring to FIG. 6, yet another option for a greenhouse is to
locate convection towers as double glass walls on the outside of the
greenhouse, and use the convection stream generated to collect CO2
on the outside. The double walls also serve to reduce the heatload on the
interior during the day and thus reduce the need for air exchange which
in turn makes it possible to maintain an elevated level of CO2 in
the greenhouse. The double glass walls also reduce heat loss during the
night.

[0057] In this example a protective glass surface 40 may be provided to
keep some of the heat away from the main roof of the glass house 42,
causing a convective flow 44 of ambient air over the roof surface. The
flow of ambient air is passed through a CO2 absorbing filter medium
46, which can by some mechanism, such as a rotating roof panel 48,
exchange places with a second like filter medium 50, where the air driven
by fan 52 on the inside of the greenhouse is passed through the filter
medium which gives up the CO, captured when the filter medium was exposed
to ambient air outside the greenhouse. Because the air inside the
greenhouse is moist, the CO2 readily is released from the filter
medium, and adds to the CO2 available in the greenhouse.

[0058] An advantage of such a unit is that it could operate at elevated
levels of CO2 without combusting fuels. Because CO2 is
delivered to the inside of the greenhouse without blowing air into the
greenhouse, this offers a possibility of reducing the exchange of air
between the outside and the inside of the greenhouse, thus improving the
heat management and moisture management of the greenhouse.

[0059] In a second exemplary embodiment of the invention, the CO2 is
extracted and delivered to an algal or bacterial bioreactor. This may be
accomplished using conventional CO2 extraction methods or by using
an improved extraction method as disclosed in our aforesaid PCT
applications or disclosed herein; e.g., by a humidity swing. A humidity
swing is advantageous for extraction of CO2 for delivery to algae
because the physical separation allows the use of any collector medium
without concern about compatibility between the medium and the algae
culture solution. Transfer of gaseous CO2 allows for the selection
of any algae species, including macro and microalgae, marine or
freshwater algae. Therefore, the selection of algae species to be grown
could be solely dependent on environmental factors and water quality at
the collector site. For example, the algae species to be used could be
selected from algae naturally occurring at the site, which are uniquely
adapted to the local atmospheric, environmental and water quality
conditions.

[0060] There are two major advantages of transferring captured CO2 in
gaseous form. The first advantage is that the collector medium and/or the
collector regeneration solution will not contact the algae culture
solution and/or algae. The second is that all species of algae are
capable of absorbing gaseous CO2.

[0061] Depending on the CO2 tolerance of particular algae cultures,
the CO2-enriched air can be pumped successively through several
algae cultures in order of decreasing CO2 tolerance and increasing
CO2 uptake efficiency. Alternatively the air can be diluted to the
optimum CO2 concentration.

[0062] Referring to FIG. 7, one embodiment of the present invention takes
advantage of the fact that gaseous CO2 can be driven off the
collector medium using a humidity swing. The humidity swing will transfer
captured CO2 as gaseous CO2 from the collector 110 into the
algae culture 116. An ion-exchange collector medium loaded with CO2
will emit gaseous CO2 when subjected to an increase in humidity or
when wetted with water. And the collector medium will absorb more gaseous
CO2 when the humidity of the CO2-supplying gas stream is
decreased and/or the collector medium dries.

[0063] The present invention provides a common headspace above the
collector medium and the algae culture. This exposes the algae to gaseous
CO2 while physically separating the collector medium from the algae
culture solution. The headspace will be sealed from ambient air. The
humidity is then raised in the closed headspace volume. Alternatively,
the collector medium may be wetted. The CO2 emitted from the
collector medium quickly diffuses through the entire headspace and
contacts the algae culture solution surface.

[0064] The CO2 is then transferred into the algae culture either via
gas diffusion or by bubbling the headspace gas through the algae culture
solution using a recirculating pump. As the algae removes the CO2
from the headspace, the collector medium continues to off gas until
equilibrium is reached. The algae culture solution can be mechanically
stirred. All other nutrients and light are provided to the algae as
needed. The algae may then be collected in an algae harvester 120.

[0065] CO2 concentrations in the headspace above wetted collector
medium are up to 20%; or 0.2 atmosphere partial pressure. The
concentration can be regulated by the volume to volume ratio of collector
medium to headspace. Also the collector medium can release 60% of the
captured CO2 during a humidity swing/wetting.

[0066] Alternatively, it is also possible to pump gas from the collector
medium volume through the algae culture in order to transfer the
CO2. If the algae pond is warm and moist the moisture from the algae
pond may be sufficient to stimulate the release of CO2 from the dry
resin, again by the humidity swing mechanism.

[0067] Referring to FIG. 8, in another embodiment of the present invention
CO2 concentrations in ambient air can saturate the ion-exchange
medium with CO2 to the level that the CO2 is bound as
bicarbonate anion. This embodiment provides regeneration of the collector
medium using an alkaline solution. During the regeneration, the anion
composition in the solution is changed to approximately 100% bicarbonate.
Aqueous bicarbonate solution is not stable under atmospheric conditions
and releases gaseous CO2. Gaseous CO2 emission can be enhanced
by bubbling the headspace air through the solution using a recirculating
pump.

[0068] An alternative embodiment provides a common headspace above the
collector regeneration solution and the algae culture solution. This
exposes the algae to gaseous CO2, while separating the regeneration
solution from the algae culture solution. In other aspects, this
headspace operates similar to the headspace for the collector medium, as
discussed above.

[0069] Referring to FIG. 9, another alternative embodiment of the present
invention uses an electrodialysis (ED) process to free gaseous CO2
from the loaded collector solution. The freed CO2 is then
transferred into an algae culture 216. The transfer of gaseous CO2
from the collector 210 to the algae culture 216 through an
electrodialysis (ED) process has the advantage that the collector
solution or sorbent and algae culture solution are physically separated
from each other at all stages of the process. This prevents the mixing of
the two solutions and also prevents ion exchange between the solutions.
The ED process has this in common with the humidity swing process. And as
in the humidity process, the physical separation allows the use of any
collector medium and any algae without regard to compatibility between
the medium and the algae culture solution.

[0070] An alternative embodiment of the invention takes advantage of the
fact that gaseous CO2 can be driven off the collector regeneration
solution using an ED process. In the ED process the loaded collector
regeneration solution is split into two streams to enter the ED cell 214.
Protons are added to the first stream across a secondary membrane 236 and
the inorganic carbon is driven off as gaseous CO2, while the sodium
cations are transferred through a cationic membrane 234 into the second
stream. In addition to the sodium ions, hydroxide ions are added to the
second stream across another secondary membrane 236 thus neutralizing the
bicarbonate in this stream to carbonate.

[0071] The first stream exits the ED cell as water or dilute sodium
bicarbonate solution while the second stream exits as a concentrated
sodium carbonate solution. The two streams are combined to form fresh
collector solution. The gaseous CO2 that is driven off the first
stream is bubbled into the algae culture and is fixated as biomass.

[0072] As inorganic carbon is removed from the brine, the solution turns
more alkaline and additional bicarbonate needs to be added to maintain
the pH. Filtration allows us to recover some of the fluid and thus return
water and sodium from the bioreactor. In one particular implementation
the electrochemical cell will run between two separate fluid cycles, one
fairly alkaline which runs between the collector and the base side of the
electrochemical cell, and the other which runs at near neutral pH between
the algae-reactor and the acidic side of the cell. Carbonic acid is
transferred from the base side to the acid side of the cell. This step
regenerates the wash and reloads the fluid with CO2.

[0073] By feeding the bicarbonate sorbent to the algae, CO2 can be
removed from the sorbent without first converting the CO2 back to
CO2 gas. Moreover, by selection of suitable sorbent material for the
air capture side, the pH of the washing fluid can be kept relatively low,
and if one uses algae that can tolerate a relatively high pH, the pH
difference that needs to be made up by electrodialysis becomes relatively
small, and in some implementations one can completely eliminate the
dialysis cell.

[0074] Referring to FIG. 10, another embodiment of the present invention
uses an ED process to decrease the bicarbonate concentration in the
collector solution and to increase the bicarbonate concentration in the
algae culture solution. The collector solution enters the ED cell 214 in
the bicarbonate state, while the algae culture solution enters the ED
cell in the carbonate state. When the fluids exit the ED cell, the
collector solution is in the carbonate state and the algae culture
solution is in the bicarbonate state.

[0075] Since cations are transferred from the algae culture solution to
the collector solution, the algae culture solution is diluted to roughly
half its normality, while the collector solution roughly doubles its
normality. To make up for the sodium imbalance, half of the loaded
collector solution (bicarbonate form) is transferred directly from the
collector to the algae culture.

[0076] In a process scheme according to the present invention, cations are
transferred from the algae solution into the collector solution through a
cation exchange membrane 234. The algae culture solution contains
predominantly sodium cations, but also potassium, magnesium and calcium
ions as well as traces of other metal cations. The potential transfer of
magnesium and calcium is of concern, since both ions form fairly
insoluble carbonates and hydroxides. The formation of these salts, also
known as scaling, can foul up the membranes in the ED cell and/or the
collector medium.

[0077] Calcium and magnesium are added to the algae culture as mineral
nutrients, at the start of an algae growing cycle. As the algae biomass
increases calcium and magnesium are taken up into the biomass and their
concentration in the algae culture solution decreases. Simultaneously,
the culture solution pH increases as the bicarbonate solution is changed
into a carbonate solution. If magnesium, calcium and carbonate ions are
present above their solubility products, chemical precipitation will
further decrease the magnesium and calcium ion concentrations.

[0078] The exhausted culture solution with decreased calcium and magnesium
concentrations and a high pH is entered into the ED cell. There the
culture solution is changed from a carbonate into a bicarbonate solution
and its pH decreases accordingly. As the carbonate ion concentration
decreases, the solution can hold more calcium and magnesium. So scaling
is unlikely to happen in this part of the ED cell.

[0079] However, at the same time, cations including calcium and magnesium
are transferred from the algae culture solution 216 to the collector
solution half-cell of the ED. In this half-cell, the bicarbonate solution
coming from the collector is changed into a carbonate solution: the
carbonate concentration and the pH increase. Further, excess H2O may
be removed from the bicarbonate solution using an osmosis cell 224.

[0080] The process is designed such that the pH of the exiting collector
solution is close to the pH of the incoming algae solution. Therefore,
scaling should not occur as long as everything is in balance. However, to
keep perfect balance may not always be practical on the macro scale, and
it may be impossible on the micro scale within the ED cell. It is
possible that micro layers or pockets with increased hydroxide or cation
concentrations are formed at the membrane surfaces. Increased
concentrations at the surface of the membranes might cause scaling in the
collector solution half-cell.

[0081] To minimize scaling, the flux of calcium and magnesium cations has
to be minimized. This is a problem well known in the manufacture of salt
from seawater, sodium hydroxide manufacture, and in processing of skim
milk by electro dialysis (T. Sata, 1972; T. Sata et al., 1979, 2001; 3.
Balster, 2006). To minimize flux, the cationic membrane that separates
the two half-cells has to be monovalent ion selective. In general, strong
acid cation exchange membranes show larger transport numbers for divalent
than monovalent ions. It is assumed that this is due to higher
electrostatic attraction with the negatively charged fixed ion exchange
sites. The prior art has shown that transport numbers for divalent
cations decrease with lower charge density on membranes.

[0082] Two commercially available highly monovalent cation selective
membranes have been identified as particularly suited for this process.
One membrane is manufactured by Asahi Glass and is traded under the name
Selemion CSV. The second is manufactured by Tokuyama Soda and is sold
under the name Neosepta® CIMS. The transport numbers (t) for Selemion
CSV are: t(Na)<0.92 and t(Ca, Mg)<0.04. The transport numbers for
Neosepta CIMS are t(Na,K)=0.90 and t(Ca, Mg)=0.10. The transport numbers
are defined as the equivalence flux of the cation divided by the total
equivalence flux during electrodialysis.

[0083] This aspect of the invention uses a monovalent cation selective
membrane to minimize the transfer of multivalent cations from the algae
culture solution into the collector regeneration solution. Any scaling
built up with time, will be removed using an acid solution.

[0084] Both the algae culture solution as well as the collector solution
will be filtered before entering the ED cell to avoid membrane fouling
with particles. Organic molecules will be scavenged from the algae
culture solution by means of organic scavenging ion exchange resins.

[0085] Referring to FIG. 11, in another embodiment of the present
invention the CO2 captured from air is transferred to the algae by
feeding the loaded collector solution 310 to the algae. The loaded
collector solution is enriched in sodium bicarbonate. Nutrients are added
to the collector solution and it becomes the feed stock for algae. In
this embodiment of the invention the solution feed is not recycled, so
that the collector solution becomes a consumable.

[0086] In this process the algae culture solution 316 would increase in
salt content as more and more sodium bicarbonate is added. The sodium
bicarbonate is changed into carbonate during algae growth. To lower the
carbonate concentration and to slow the salting, some of the remaining
nutrients can be added as acids instead as sodium salts, which will
convert carbonate ions to bicarbonate and minimize the addition of
sodium.

[0087] Alternatively, the sodium bicarbonate sorbent is fed directly to an
algae-reactor to supply the algae with CO2, and the algae is removed
for further processing, with the sodium carbonate being returned to the
air extraction station.

[0088] Many algae can utilize bicarbonate as their carbon source. Also,
some algae prefer bicarbonate over CO2 as their carbon source. These
are often algae that are indigenous to alkaline lakes, where inorganic
carbon is predominantly present as bicarbonate. These algae can tolerate
large swings in pH of 8.5 up to 11. Other algae can utilize
HCO3- as their carbon source, but require pH ranges below pH=9,
which would require bubbling CO2 through the bicarbonate/carbonate
solution.

[0089] Algae use the carbon source to produce biomass through
photosynthesis. Since photosynthesis requires CO2 not bicarbonate,
the algae catalyze the following reaction:

HCO3-CO2+OH.sup.

[0090] In the presence of HCO3-, this becomes:

HCO3-+OH-→CO3-2+H2O

[0091] Algae growth in a bicarbonate solution induces the following
changes in the solution: (1) a decrease in HCO3- concentration;
(2) an increase in CO3-2 concentration; and (3) an increase in
pH.

[0092] Another embodiment the present invention uses an algae culture
solution for collector regeneration. The collector medium in the
carbonate form can absorb gaseous CO2 from ambient air until the
anion composition of the medium is nearly 100% bicarbonate. In this state
the collector medium is fully loaded and CO2 absorption comes to a
halt. A carbonate solution can be used in regeneration to return the
loaded collector medium to a carbonate form through ion exchange. The
anion composition of the regeneration solution can be changed from 100%
carbonate to nearly 100% bicarbonate through anion exchange with the
fully loaded collector medium. In a counter-flow regeneration process the
collector medium can be brought into a carbonate form, while the
carbonate regeneration solution is changed into a bicarbonate solution.
The regeneration solution is fully loaded when it is in the bicarbonate
form, since it cannot remove any more bicarbonate from the collector
medium.

[0093] The algae are introduced into the process to remove the captured
CO2 from the loaded regeneration solution by bicarbonate dehydration
and neutralization (see above). The algae utilize the freed CO2 for
biomass growth. And the regeneration solution is changed from bicarbonate
back into a carbonate solution.

[0094] In this process, the carbonate regeneration solution and the
collector medium are recycled, while ambient air CO2 is changed into
algal biomass. This is shown in FIG. 11.

[0095] This process provides a cycle in which the ion exchange collector
medium absorbs air CO2. During the absorption the collector medium
changes from carbonate to bicarbonate form. Then the regeneration
solution pulls the air CO2 from the loaded collector medium. In this
exchange the collector medium is changed back into its carbonate form,
while the regeneration solution changes from a carbonate to a bicarbonate
solution. Finally, the algae remove the air CO2 from the loaded
regeneration solution by fixating it into biomass. In this step, the
algae catalyze the reaction from bicarbonate to CO2 and carbonate.
The CO2 carbon is bound into the algae biomass. The carbonate is
left in solution. The resulting regeneration solution is then in
carbonate form.

[0096] In another embodiment of the present invention, the algae culture
solution is used as the collector regeneration solution. This means that
the collector regeneration solution will in addition to carbonate contain
other nutrients as required for the algae. Amongst these nutrients are
anions that will compete with the carbonate anion during ion exchange
with the collector medium.

[0097] In this process diatoms will not be used, since they require
silica, which cannot be efficiently removed from the collector medium
with a carbonate wash.

[0098] Other anionic nutrients typically found in algae culture mediums
are: nitrate (NO3-), sulfate (SO4-2), and phosphate
(PO4-3). Phosphorus may also be present as dibasic
(HPO4-) or monobasic phosphate (H2PO4-)
depending on pH.

[0100] However, the prior art has shown that algae can grow at much lower
nutrient concentrations than are contained in typical culture mediums.

[0101] To estimate the effect of the nutrient concentrations on the
collector medium a nutrient-containing regeneration solution was mixed as
follows: 0.14 M CO3-2, 0.04 M NO3-, 0.0017 M
SO4-2 and 0.0017 M H2PO4-. These represent the
highest concentrations to be found in an algae culture medium and,
therefore the worst-case scenario.

[0102] The collector medium was then flushed with this `worst-ease`
solution until equilibrium was reached between the solution and the
collector medium. At the pH of carbonate solution, phosphorus is present
as dibasic phosphate (HPO4-2). Dibasic phosphate is basic
enough to absorb CO2. Therefore, the presence of dibasic phosphate
anions on the collector medium will not lower the medium's CO2
uptake capacity. It was determined that at equilibrium, about 50% of the
collector medium's total exchange sites were occupied by carbonate and
phosphate ions and 50% by nitrate and sulfate. Although the other
nutrients outnumber carbonate, they do not completely replace it;
instead, an anion equilibrium is reached that does not change with
application of additional volumes of solution to the collector medium.

[0103] The experiments showed that in a worst-case scenario, the collector
medium looses approximately 50% of its CO2 uptake capacity. However,
as determined by the research cited above, the nutrient concentrations in
the solution can be depleted significantly during algae growth. For
example, nitrate being by far the most abundant nutrient after inorganic
carbon, can be reduced to 0.002 M, a mere 5% of the concentration used in
the worst-case scenario experiment. And phosphate is reduced to 45% of
the worst-case scenario.

[0104] Further, a collector medium washed with a nutrient-depleted
solution will loose about 20% of its CO2-uptake capacity. It is
therefore possible to use the collector medium and wash it with a
carbonate solution that has been derived from the algae growth medium.

[0105] The algae will secrete or release organic compounds into the
solution during metabolism or decay. These organics will be scavenged
from the solution, prior to applying the solution to the collector
medium. Organics scavenging may be done with an adsorbent-type ion
exchange resin or other processes.

[0106] Diatoms will not be used in this process, since they require
silica, which cannot be efficiently removed from the collector medium
using a carbonate wash.

[0107] A preferred algae for the present embodiment will have the
following characteristics: they are adapted to high ionic strength
liquids; they can grow in a pit range of 8.5 to roughly 11; they can
tolerate a gradual pH change; they can use bicarbonate as their carbon
source; they need little silica as a nutrient; they are capable of
changing the pH of a solution from 8.5 to 11 or above; they can diminish
nutrient concentrations to low levels; they can be used in biochemistry,
agriculture, aquaculture, food, biofuels, etc.

[0108] Good candidates are, but are not limited to, algae that live in
alkaline waters such as Spirulina platensis, Spirulina fusiformis,
Spirulina sp., Tetraedron minimum and others.

[0109] There are many alternatives for this embodiment. Loaded collector
solution (bicarbonate solution depleted in nutrients) is added to an
algae culture together with fresh nutrients; the algal culture utilizes
bicarbonate as its inorganic carbon source, by taking up about 50% of the
bicarbonate carbon into its biomass and changing the remaining 50% to
carbonate anions. Simultaneously, the algae culture depletes the nutrient
concentrations in the solution. The culture is filtered, harvesting the
algae biomass, while shunting the nutrient depleted solution towards the
CO2 collector. The nutrient depleted solution is cleaned of organics
and other materials deleterious to the collector medium. The solution now
enriched in carbonate is used to regenerate the collector. In the process
each carbonate anion is replaced by two bicarbonate anions, until the
collector solution is loaded. The loaded collector solution is added to
the algae culture together with fresh nutrients as mentioned above.

[0110] The process can be run as a continuous loop or a batch process,
whichever is more practical given location, algae type, etc. The process
can employ algae culturing technologies already in use and proven or new
technologies. For example, outdoor ponds have proven successful for the
cultivation of Spirulina, Chlorella vulgaris, Ankistrodesmus braunii and
other species in California, Hawaii, the Philippines and Mexico among
other places. According to the National Renewable Energy Laboratory
(NREL), outdoor ponds, e.g. so-called "race ponds", are the most
efficient methods for growing a large biomass of algae.

[0111] The cultivation may use solar energy, artificial lighting or both
dependent on the algae species and the place of operation. Algae culture
solutions may be stirred to return algae to the zone of highest light
ingress. Or the light might be brought into the algae cultures through
mirrors, fiber optics and other means.

[0112] The algae can be either suspended in solution or immobilized. When
suspended, algae follow their own growth patterns: single cells,
colonies, clumped and so on. The natural growth pattern may not be the
best match for the technology used. For example, small single celled
algae may require elaborate harvesting processes.

[0113] Algae may naturally grow immobilized, if they attach themselves to
surfaces, e.g., macro algae. Or algae can be immobilized: in beads using
k-carragenan or sodium alginate, in polyurethane foam, on filter
material, or as biofilms on column packing, or in other ways.

[0114] In an immobilized state, the algae may still be suspended, for
example in bead form, and moving with the solution. Alternatively, the
immobilized algae may be stationary in a column or other device, while
the solution percolates past.

[0115] In another embodiment of the present invention, the collector
medium is immersed into the Algae Culture. This can be done either in a
batch process or in a continuous process. In a batch process, a batch of
collector medium is alternatingly immersed in the algae culture and
exposed to ambient air. In a continuous process, collector medium is
continuously moved along a path on which it is alternatingly immersed in
the algae culture or in exposed to air. The easiest implementation would
be a disk of collector medium that rotates continuously around its
center. The disk is submerged up to its center point in the algae
culture, so that, at any time, one half of the collector medium is
submerged in the liquid and the other half is exposed to air.

[0116] In this embodiment of the invention, collector medium could
potentially be immersed in the algae culture solution at times of high
nutrient content and at times of low nutrient content. The CO2
capacity of the collector medium will, therefore, range from 50% to 80%
of its full capacity. Air exposure times can be adjusted to account for
the capacity decrease.

[0117] Referring to FIG. 12, another embodiment of the present invention
discloses sodium bicarbonate transferred from the collector solution to
the algae by washing the algae in the loaded collector solution. However,
nutrients will not be added to the collector solution. Instead, nutrients
will be provided to the algae via a second separate wash cycle consisting
of nutrient-rich carbon deficient solution.

[0118] In this process the algae will be immersed in nutrient-deficient
bicarbonate solution (loaded collector solution) alternating with
inorganic carbon-deficient nutrient solution 326. A short rinse cycle
will be employed between washes. The rinse will be added to the solution
of the preceding wash.

[0119] The cycles of nutrient and bicarbonate washes will be optimized for
the algae species used. One or more algae species may be used either
mixed or in series to optimize the conversion of the bicarbonate solution
(loaded collector solution) to carbonate solution (fresh collector
solution). The fresh collector solution may be filtered to remove
particles and cleaned of organic molecules or other deleterious content
prior to application on the collector medium.

[0120] The process can be designed to utilize suspended algae or
immobilized algae. If the algae are suspended, the process has to be run
as a batch process, and the algae have to be filtered from the solution.
To ease filtering the algae may be "immobilized" in suspended beads, in
order to increase the particle size.

[0121] A process involving immobilized algae can utilize algae that
naturally grow immobilized, for example macro-algae that attach
themselves to surfaces, or micro-algae that form biofilms etc.

[0122] In addition to others methods disclosed elsewhere in this
application, the algae could be immobilized in columns, inclined
raceways, ponds or other containers. The containers may be arranged to
allow gravitational fluid flow. Immobilization may be on the container
walls and floors and/or on structures such as plates, packing etc.
installed therein. Light is brought into the containers as needed either
by natural lighting, artificial lighting, mirrors, fiber optics, etc.

[0123] Referring to FIG. 13, another embodiment of the present invention
transfers gaseous CO2 from the loaded collector solution 410 to the
algae culture solution 416 through a hydrophobic microporous membrane
434. Gaseous CO2 can be transmitted from a bicarbonate solution
through a hydrophobic membrane into a carbonate solution; and that the
CO2 partial pressure differential between the two liquid streams is
sufficient to drive the transfer. A transfer of water was noted from the
more dilute solution to the more concentrated solution. As the membrane
is hydrophobic, the transfer is of gaseous water molecules.

[0124] Simplified, the process can be described as two half-cells
separated by a microporous, hydrophobic membrane. The first half cell 438
holds the loaded collector solution (sodium bicarbonate solution); while
the second half cell 418 holds the algae culture (sodium carbonate
solution including nutrients and algae).

[0125] The collector solution half-cell reaction is defined as follows:

2HCO3-(aq)→CO2(g)+CO3-2(aq)+H2O

This is followed by CO2(g) diffusion through membrane into the algae
culture half-cell. The reaction in the algae culture half-cell will
follow in one of two ways:

Algae consume CO2(g)

or

CO3-2(aq)+CO2(g)+H2O →2HCO3-(aq)

and

HCO3-(aq)+OH-→CO3-2(aq)+H2O

[0126] As can be seen from the half-cell reactions, the pH in the
collector solution will continuously increase as bicarbonate is reacted
into carbonate through off-gassing of gaseous CO2. In a balanced
system the algae culture solution will not change its pH as the gaseous
CO2 is fixated by algae growth into biomass. The algae culture will
preferably be close to a carbonate solution. In that case, it would not
contain appreciable amounts of bicarbonate. This condition would maximize
the gaseous CO2 partial pressure differential between the collector
solution and the algae culture.

[0127] The physical arrangement of the two half-cells can take many forms
including but not limited to the few arrangements described herein. Each
arrangement will optimize the ratio of liquid-membrane contact area to
solution volume. In general it is advantageous to run the collector
solution through membrane channels submerged in the algae culture, since
this will enable light supply to the algae culture. In cases where the
algae culture is contained in membrane conduits, light will be supplied
inside the conduits.

[0128] The membrane conduits can take many shapes. For example, they can
be parallel membrane sheets, causing a sheet flow of solution sandwiched
between the membranes. Or they could be tubular with the tube
cross-section taking varying forms, for example round, square,
rectangular, corrugated, etc. Tubes could form a spiral or other shapes
to increase their path length through the solution.

[0129] The process can be run as a batch procedure, a continuous loop
process or any combination thereof. Light and nutrients will be supplied
as needed.

[0130] In a pure batch process, a batch of loaded collector solution is
brought in membrane contact with a batch of algae culture and left to
reach equilibrium.

[0131] In a pure continuous loop process both solutions flow in continuous
loops. The loaded collector solution would flow along a membrane path,
throughout which it transfers its gaseous CO2 to the algae solution;
from there it enters the regeneration system for the collector medium,
where it loads up with CO2 to then reenter the membrane conduit. The
algae solution will flow past the membrane path with algae fixating the
gaseous CO2; from there it will enter a harvesting system 420, where
some or all algae are removed from the solution to then reenter the
membrane system for renewed CO2 fixation and algae growth.
Continuous flow or loop processes may use concurrent flow or
counter-current flow of the two streams.

[0132] The major advantage of transferring the CO2 through a
hydrophobic membrane is that ions cannot cross from the algae culture
into the collector solution. The cations contained in the algae solution
include earth alkali metals that can cause scaling along the collector
solution path as the pH increases. The anions, such as nitrate and
sulfate, contained in the algae solution compete with carbonate on the
collector medium thus lowering the CO2 holding capacity of the
collector medium. Therefore, it is advantageous to keep the ions from
entering the collector solution. Since ions, which constitute the
nutrients for the algae, cannot cross into the collector solution, the
nutrient content of the algae culture can be permanently kept at the
optimum concentration for algae growth.

[0133] In addition, the prior art discloses hydrophobic membranes that are
also organophobic and can impede the transfer of organic molecules from
the algae solution to the collector solution. Any organics that may be
transferred into the collector solution will be removed from the
collector solution before it enters the collector medium. For example,
this can be done by scavenging the organic compounds onto ion exchange
resins.

[0134] The membrane will be selected for its hydrophobicity, CO2
permeability, organophobicity, and water break-through pressure. The
preferred algae for this process are those that thrive in carbonate
solutions and can both utilize gaseous CO2 and bicarbonate. However,
other algae can also be used to optimize the complete process.

[0135] Referring to FIG. 14, another embodiment of the present invention
transfers bicarbonate from the collector solution 410 into the algae
culture solution 418 through an anion permeable membrane. The collector
solution is brought into contact with one side of the anion permeable
membrane 434, while the algae culture solution is brought into contact
with the other side of the membrane.

[0136] The solutions exchange anions along concentration gradients. To
optimize this ion exchange, the solutions can be run past the membrane in
a counter-current. The solutions can also be run co-current to optimize
other parts of the system. Alternatively, the process can be set up as a
batch process rather than a continuous flow process.

[0137] The algae culture solution can be entered into the anion exchange
process with algae suspended in the solution or without the algae. See
FIG. 15. Dissolved organic compounds can be removed from the algae
culture solution prior to entering the membrane chamber.

[0138] Nutrient effects apply as discussed above. If the whole algae
culture including algae is entered into the membrane exchanger, the
nutrient concentration will be high and the collector solution will gain
high nutrient concentrations. This may lead to a reduction in the
collector medium's CO2 uptake capacity of up to 50%. If the culture
solution without algae is entered into the membrane exchanger, the
process can be set up such that nutrient-depleted solution is entered, in
which case the collector capacity might be reduced by up to 20%.

[0139] Cations will not be exchanged between the two solutions, which
greatly reduces the potential for scaling.

[0140] Alternatively, one can inject captured CO2 directly into an
algae-bio-reactor synthetic fuel production unit. A particularly simple
design is to provide a paddle wheel or disks or the like carrying
humidity sensitive ion exchange resins that are exposed primarily above
the water surface where CO2 is extracted from the air, and are
slowly rotated to dip a portion under the water surface where the
CO2 is released to provide high air-to-water transfer rates for the
CO2.

[0141] Referring to FIG. 16, in another embodiment it is possible to
shower an ion exchange resin with slightly alkaline wash water at an
extraction station 140, similar to the first exemplary embodiment, to
make up evaporative or production losses of water from the bioreactor. As
the wash water trickles over the primary resin, it will pick up bound
CO2 and dribble it into the bioreactor system 142.

[0142] Alternatively, as shown in FIG. 17, resins 142 may be added to the
water at night to retain the CO2 that may be lost from the algae due
to respiration. Thus we can improve the CO2 uptake efficiency of the
algae, by preventing the release of nighttime CO2 from the
bioreactor. In such embodiment, a secondary resin acts as a carbon buffer
in the system. At night this buffer stores the CO2 released by the
algae, while during the day it provides CO2 to the algae, while its
CO2 content may be supplemented by the CO2 that is collected by
the air collector. Once captured, the CO2 is transferred to the
resin from a more concentrated wash used in regenerating the primary
resin. Water filtration to keep algae out of the air collector generally
is not a problem due to the fact that the air-side primary resin is
designed to completely dry out in between cycles.

[0143] This transfer to the secondary resin also could be accomplished
without direct contact in a low-pressure closed moist system, such as
shown in FIG. 1, by performing a humidity swing that avoids direct
contact with the water. While such a system loses the aforementioned
advantage of not bringing CO2 back to the gas phase, it will have
other advantages in buffering the algae pond at a constant pH, without
the use of chemicals.

[0144] In a preferred embodiment of the invention, as seen in FIG. 18, in
order to reduce water losses, increase yield, and better confine the
algae, we employ bioreactors 150 with light concentrators 152. Such
systems may be built from glass tubes surrounded by mirrors, or mirror or
reflector systems that feed into fiber optic light pipes that distribute
the light throughout a large liquid volume. The advantage of the use of a
bioreactor with light concentrators is that they greatly reduce the water
surface and thus reduce water losses. Thus, the CO2, can be
collected nearby without directly interfering with the algae reactors.
Indeed air collectors could take advantage of mirror systems for guiding
air flows.

[0145] Algae typically fixate CO2 during times of light influx, and
respire CO2 during dark cycles. The CO2 is captured by adding
additional collector medium to the system in strategic places. The
collector medium can, for example, be immersed in the algae culture. In
this case, it will store bicarbonate and release carbonate during
respiration as the culture solution pH decreases, and it will release
bicarbonate and store carbonate during photosynthesis as the culture
solution increases in pH.

[0146] Collector medium can also be placed in the air space in proximity
of the algae culture to absorb CO2 that has been released from the
culture solution. This will be especially efficient in closed structures.
Collector medium placed in the proximity of the culture solution will be
regenerated using one of the processes described above.

[0147] This application is intended to include any combination of the
inorganic carbon transfer methods described in this patent using any
combination of algae cultures as required to optimize the process.
Optimization includes but is not limited to optimization of the carbon
transfer efficiency, carbon transfer rate, market value of the biomass
(for example oil content, starch content etc.), algae productivity
efficiency, and algae growth rate under any climate conditions or
climate-controlled conditions.

[0148] While the invention has been described in connection with a
preferred embodiment employing a humidity sensitive ion exchange resin
material for extracting CO2 from ambient air and delivering the
extracted CO2 to a greenhouse by humidity swing, advantages with the
present invention may be realized by extracting carbon dioxide from
ambient air using a sorbent in accordance with the several schemes
described in our aforesaid PCT Application Nos. PCT/US05/29979 and
PCT/US06/029238 (Attorney Docket Global 05.02 PCT), and releasing the
extracted CO2 into a greenhouse by suitably manipulating the
sorbent.